Engine control

Abstract

It is known that overshoot in fuel flow rate as a result of compensating for engine heat soak effects can create transient over values in desired thrust parameters. These over values may be displayed and/or utilised in other engine control systems, and although transient may create problems within the engine and apprehension with a user. By adjusting the normally calculated fuel flow rate to a fuel regulator by the introduction of a fuel flow adjustment dependent upon a variable which is related to heat soak effects it is possible to reduce the extent of overshoot as well as the transient time period of that overshoot to ongoing operational state. The variable used may be direct or indirect and will generally utilise a temperature sensor within the engine and/or other engine control procedures which may be extrapolated from such sensor values to provide a variable for heat soak compensation.

1. An engine control method for a gas turbine engine, the method comprising:
 operating a gas turbine engine at a first thrust setting demanding a first normal fuel flow and having a first engine operating temperature; 
 increasing the thrust to a second thrust setting and operating the gas turbine engine at a steady state, the second thrust setting demanding a second normal fuel flow and having a second engine operating temperature, the second engine operating temperature being greater than the first engine operating temperature; 
 obtaining at least one engine temperature dependent variable of the engine and using the engine temperature dependent variable to determine a heat soak fuel flow to account for a thermal inertia of raising an operating temperature of the engine from the first operating temperature to the second operating temperature; and 
 adjusting said second normal fuel flow by subtracting the heat soak fuel flow from said second normal fuel flow to reduce a size and duration of overshoot of power or thrust of the engine while operating the engine at the steady state. 
 
     
     
       2. A method as claimed in  claim 1  wherein the engine temperature dependent variable is obtained by directly monitoring the temperature of an engine component using a sensor. 
     
     
       3. A method as claimed in  claim 1  wherein the engine temperature dependent variable is indirectly obtained by measuring a temperature of a gas flow through the engine and extrapolating a temperature of the engine from the temperature of the gas flow. 
     
     
       4. A method as claimed in  claim 3 , wherein the temperature of the gas flow is obtained using a sensor disposed at an entrance to a combustion chamber for the engine. 
     
     
       5. An engine control method for a gas turbine engine, the method comprising:
 operating a gas turbine engine at a first thrust setting demanding a first normal fuel flow and having a first engine operating temperature; 
 changing the thrust to a second thrust setting and operating the gas turbine engine at a steady state, the second thrust setting demanding a second normal fuel flow and having a second engine operating temperature; 
 obtaining an engine temperature dependent variable of the engine and using the engine temperature dependent variable to determine a heat soak fuel flow to account for a thermal inertia of changing an operating temperature of the engine from the first operating temperature to the second operating temperature; and 
 adjusting the second normal fuel flow by subtracting or adding the heat soak fuel flow to said second normal fuel flow. 
 
     
     
       6. An engine control method according to  claim 5 , wherein the second thrust setting and second operating temperature are lower than the first thrust setting and first operating temperature so that the second normal fuel flow is adjusted by adding the heat soak fuel to the second normal fuel flow. 
     
     
       7. An engine control method according to  claim 5 , wherein the engine temperature dependent variable is obtained by directly monitoring the temperature of an engine component using a sensor. 
     
     
       8. An engine control method according to  claim 5 , wherein the engine temperature dependent variable is indirectly obtained by measuring a temperature of a gas flow through the engine and extrapolating a temperature of the engine from the temperature of the gas flow. 
     
     
       9. An engine control method according to  claim 8 , wherein the temperature of the gas flow is obtained using a sensor disposed at an entrance to a combustion chamber for the engine.